Today's communication networks provide transport of voice, video and data to both residential and commercial customers, with more and more of those customers being connected by fiber optic cables. In these communication networks, information is transmitted from one location to another by sending pulses of light through the fiber optic cables. Fiber optic transmission provides several advantages over electrical transmission techniques, such as increased bandwidth and lower losses.
Several standards for optical network communications have been developed. One example is the standard for 1-Gbit/second (Gbps) Ethernet Passive Optical Networks, often referred to as 1G-EPON. This standard was ratified as the IEEE 802.3ah standard. Another example is the related standard for 10-Gbit/second Ethernet Passive Optical Networks, referred to as 10G-EPON, which was ratified as the IEEE 802.3av standard. The latter standard supports simultaneous operation of 1 Gbps and 10 Gbps, in both directions, on the same optical fiber plant. In the downstream, or forward, direction, the 10G and 1G signals are sent in the 1575-1580 nanometer band and the 1480-1500 nanometer band, respectively, while the 10G and 1G signals in the upstream, or return, direction occupy the 1260 to 1280 nanometer band and the 1260 to 1360 nanometer band, respectively. (Narrower bandwidth signals are often used in practice.) It will be noted that the upstream bands overlap—as a result, time-division multiplexing is used to separate the 10G and 1G signals in the upstream. FIG. 1 illustrates the forward and return bands for 10G and 1G services.
Coarse Wavelength Division Multiplexing (CWDM) refers to a different set of technologies for carrying multiple optical signals on a single fiber. CWDM systems have channels spaced at 20 nanometers. 18 channels have been specified, at wavelengths ranging from 1270 nanometers to 1610 nanometers. (See the International Telecommunications specification ITU-T G.694.2, “Spectral Grids for WDM Applications: CWDM Wavelength Grid,” for additional details.) Eight of these channels are commonly used, at wavelengths of 1470, 1490, 1510, 1530, 1550, 1570, 1590, and 1610 nanometers.
Communications service providers may serve customers with either EPON links, or CWDM links, or both. In scenarios where a communication service provider wishes to provide services using both groups of technologies, optical equipment and fibers may be duplicated. This increases the costs of the operator's network and the physical sizes of the various components. Accordingly, improved techniques and devices for combining multiple optical communications technologies are needed.